Synthesis, crystal structure, and reactivity of alkali and silver salts of sulfonated imidazoles

Both 2-methylimidazole and 2-ethyl-4-methylimidazole were monosulfonated with oleum in the five position. In crystals of the monohydrate of 2-methylimidazole-5-sulfonic acid, hydrogen bonds link the molecules into a 3-dimensional network, while in crystals of 2-ethyl-4-methylimidazole-5-sulfonic acid, corrugated 2-dimensional layers are present. The Li and Ag salts and the bis(trimethylsilyl) derivatives of 2-ethyl-4-methylimidazole-5-sulfonic acid were prepared, and there is evidence for doubly deprotonated imidazolesulfonate in aqueous solution. The monohydrate of the Li salt and the Ag salt also form a 3-dimensional, H-bonded network. Only in the Ag salt does the asymmetric unit consist of more than one basic formula unit. One Ag atom is 2-coordinate and links two nitrogen atoms, while the other Ag atom has distorted tetrahedral coordination and links the sulfonate groups into an infinite chain. Reactions of the silver salt with 1,4-dibromobutane in non-protic solvents such as 1-methyl-2-pyrrolidone were used to link two of the imidazolesulfonic acid units with a 4-carbon chain at the nitrogens.

Graphical abstractThe synthesis and crystal structures of 2-methylimidazole-5-sulfonic acid, 2-ethyl-4-methylimidazole-5-sulfonic acid, and the Li, Ag, and bis(trimethylsilyl) derivatives of the latter are described. Silver 2-ethyl-4-methylimidazole-5-sulfonate (pictured) is a three-dimensional network in the crystal assembled by bonds between 2-coordinate Ag and N, 4-coordinate Ag and O, and by hydrogen bonding.Figure optionsDownload full-size imageDownload as PowerPoint slide